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Q45H Training Handout 4.05
Page 3 of 11
Chlorine Calibration
Once power is applied and sample water is running past the sensor (via the flow cell) a good 6-8 hours should be
allowed for complete polarization ‘of a brand new sensor’ (unless using the polarizer as above) re-builds after this time
should only take about 15 – 20 minutes. It is generally unnecessary to set the zero at start up and/or every calibration;
however, it should be checked in the MEASURE display, go UP to see zero = 0.00 an (if greater than +/-25nA, an
electronic zero
cannot
be carried out) see
chlorine zero cal
below.
There are two options in the chlorine calibration menu, “1 Ref” and “2 Zer”
1
Ref
Used to set the monitor to read the same as manual sample (e.g. Palin or Hach test with DPD) during
calibration
2
Zer
Used to check the zero offset of the sensor. Zero offsets on ATi sensor are very stable and it is not
necessary to re zero the sensors before every calibration
Chlorine Zero Cal
“2 Zer”
Chlorine sensors have extremely low offset currents at zero. For this reason, it is normally sufficient to simply leave the
zero at the factory default of 0.0 nA. As an alternative, an electronic zero can be set by disconnecting the sensor from
the cable.
The steps below assume that the sensor has been prepared in accordance with page 2, Chlorine Sensor Assembly. Note
that the 8 hour waiting time in step 2 below is not required if the monitor has been running for 8 hours prior to power
and water sample flowing. If the unit has been running with the sensor connected, the sensor will normally return to a
stable zero within 15 minutes.
1.
If the sensor requires zeroing simply go to the MEASURE mode, press the UP arrow until it reads ‘zero = ? n/A
2.
Now disconnect the chlorine sensor and watch the readings drop to zero (leave for a couple of minutes to allow a
stable zero.
3.
Scroll to the CAL menu section using the MENU key and press ENTER or the UP arrow key.
Cal Chlor
will then be
displayed.
4.
Press the ENTER key. The screen will display a flashing
1-Ref
for span calibration or a
2-Zer
for zero calibration.
Using the UP arrow key, set for a
2-Zer
zero calibration and press ENTER.
5.
The system now begins acquiring data for the sensor zero calibration value. As data is gathered, the units for sensor
current in nanoamps (nA) and temperature may flash. Flashing units indicate that this parameter is unstable. The
calibration data point acquisition will stop only when the data remains stable for a pre-determined amount of time.
This can be overridden by pressing ENTER. If the data remains unstable for 10 minutes, the calibration will fail and
the message
Cal
Unstable
will be displayed.
If accepted, the screen will display the message
PASS
with the new sensor zero reading (offset), then it will return
to the main measurement display. If the calibration fails, a message indicating the cause of the failure will be
displayed and the FAIL icon will be turned on. The range of acceptable value for sensor offset is -25 nA to +25 nA.
Should a FAIL occur, carefully inspect the sensor for a tear in the membrane. It will probably be necessary to rebuild
the sensor as described on page 2, Chlorine Sensor Assembly. Should the offset value remain high and result in
calibration failures, review the Service section of this manual, and then contact the service dept. at ATI for further
assistance.
The sensor zero offset value in nA from the last zero calibration is displayed on the lower line of the Default Menus
for information purposes.
